This invention relates to long-chain polyether polyols having a high content of primary Oh groups as well as a process for their production by means of double-metal cyanide (DMC) catalysis.
Long-chain polyether polyols having high contents of primary OH groups are required for many polyurethane applications. They are used, for example, in hot and cold mould foaming and in RIM applications (see, for example, Gum, Riese, Ulrich (Eds.): xe2x80x9cReaction Polymersxe2x80x9d, Hanser Verlag, Munich, 1992, p.67-70). Long-chain polyether polyols having high contents of primary OH groups are conventionally produced in a two-step process, wherein first of all propylene oxide (or a mixture of propylene oxide and ethylene oxide) is polymerised in the presence of starter compounds having active hydrogen atoms and of a basic catalyst, with a polyether polyol having mainly secondary OH groups being obtained. In the second step, the so-called EO tip, ethylene oxide is then added to the basic polymer, the majority of the secondary OH groups being converted into primary OH groups. In this process the same basic catalyst (for example, KOH) is conventionally used for the propoxylation reaction and for the ethoxylation reaction.
Double-metal cyanide (DMC) catalysts for the production of polyether polyols have been known for a long time (see, for example, U.S. Pat. No. 3,404,109, U.S. Pat. No. 3,829,505, U.S. Pat. No. 3,941,849 and U.S. Pat. No. 5,158,922). Compared with the conventional production of polyether polyols by means of basic catalysts, the use of these DMC catalysts for the production of polyether polyols brings about in particular a decrease in the content of monofunctional polyethers with terminal double bonds, so-called monools. The polyether polyols thus obtained can be processed to form high-quality polyurethanes (for example, elastomers, foams, coatings). Improved DMC catalysts, of the type described, for example, in EP-A 700,949, EP-A 761,708, WO 97/40086, WO98/16310, DE-A 197 45 120, DE-A 197 57 574 and DE-A 198,102,269, possess in addition an exceptionally high activity and render possible the production of polyether polyols at very low concentrations of catalyst (25 ppm or less), so that a separation of the catalyst from the polyol is no longer necessary.
A disadvantage in the use of DMC catalysts for the production of polyether polyols is that with these catalysts, unlike basic catalysts, a direct EO tip is not possible. If ethylene oxide (EO) is added to a poly(oxypropylene) polyol containing a DMC catalyst, the result is a heterogeneous mixture which consists for the most part of unreacted poly(oxypropylene) polyol (having mainly secondary OH groups) and to a small extent of highly ethoxylated poly(oxypropylene) polyol and/or polyethylene oxide. The conventional way of obtaining DMC polyols having a high content of primary OH groups consists, therefore, in carrying out the EO tip in a second, separate step by means of conventional base catalysis (for example, KOH catalysis) (see, for example, U.S. Pat. No. 4,355,188, U.S. Pat. No. 4,721,818, EP-A 750,001). A particular disadvantage of this two-step process is that the basic polymer obtained in the process has to be worked up in a very expensive way, for example, by neutralisation, filtration and dehydration.
U.S. Pat. No. 5,648,559 discloses poly(oxyalkylene) polyols having poly(oxypropylene/-oxyethylene) end blocks, the polyols being produced by DMC catalysis and having a content of primary hydroxyl groups of  less than 50 mol-%. The maximum total content of oxyethylene units in these polyols is 20 wt. %. U.S. Pat. No. 5,700,847 describes poly(oxyalkylene) polyols having up to 25 wt. % oxyethylene units, the latter being containable in mixed blocks or pure poly(oxyethylene) end blocks. The polyols produced without EO tip have  less than 50 mol % of primary OH groups. In U.S. Pat. No. 5,668,191, likewise poly(oxyalkylene) polyols having a maximum of 20 wt. % oxyethylene units and less than 50 mol % of primary hydroxyl groups are used.
It has now been found that long-chain polyether polyols having a content of primary OH groups of  greater than 50 mol-% can be obtained by DMC-catalysed polyaddition of an ethylene oxide (EO)/propylene oxide (PO) mixture as an end block to starter compounds having active hydrogen atoms, if the total content of oxyethylene units in the polyol is established at more than 25 wt. %.
The present invention provides long-chain polyether polyols having a content of primary OH groups of 40 to 95 mol-%, preferably 50 to 90 mol %, and a total content of oxyethylene units of more than 25 wt. %, preferably more than 30 wt. %, particularly preferably more than 35 wt. %, which have a poly(oxyethylene/-oxypropylene) end block produced in the presence of a DMC catalyst.
The invention also provides a process for producing the polyols according to the invention by polyaddition of an ethylene oxide (EO)/propylene oxide (PO) mixture in the weight ratio EO:PO of 40:60 to 95:5, preferably 50:50 to 90:10, particularly preferably 60:40 to 90:10, in the presence of DMC catalysts, as an end block to starter compounds having active hydrogen atoms.
The DMC catalysts which are suitable for the process according to the invention are known in principle and are described in detail in the prior art cited above. It is preferable to use improved, highly active DMC catalysts, which are described, for example, in EP-A 700,949, EP-A 761,708, WO 97/40086, WO98/16310, DE-A 197 45 120, DE-A 197 57 574 and DE-A 198,102,269. Typical examples are the DMC catalysts described in EP-A 700,949 which, besides a double-metal cyanide compound (for example, zinc hexacyanocobaltate(III)) and an organic complexing ligand (for example, tert. butanol), also contain a polyether having a number average molecular weight of more than 500 g/mol.
The compounds used as starter compounds having active hydrogen atoms are preferably those with molecular weights of 18 to 2,000 g/mol, preferably 200 to 2,000 g/mol and 1 to 8, preferably 2 to 6, hydroxyl groups. Examples which may be given are butanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,6-hexanediol, bisphenol A, trimethylolpropane, glycerol, pentaerythritol, sorbitol, cane sugar, degraded starch or water.
It is more advantageous to use those starter compounds having active hydrogen atoms which have been prepared from the above-mentioned low-molecular starters, for example, by conventional alkaline catalysis and are oligomeric alkoxylation products with number average molecular weights of 200 to 2,000 g/mol.
Compounds preferably used are oligonmeric propoxylated starter compounds having 1 to 8 hydroxyl groups, particularly preferably 2 to 6 hydroxyl groups, and number average molecular weights of 200 to 2,000 g/mol.
By DMC-catalysed polyaddition to an ethylene oxide/propylene oxide mixture in the weight ratio EO:PO of 40:60 to 95:5, preferably 50:50 to 90:10, particularly preferably 60:40 to 90:10, as end block, the starter compounds having active hydrogen atoms can be directly converted into a long-chain polyether polyol having a high content of primary OH groups and a content of oxyethylene units of  greater than 25 wt. %, preferably  greater than 30 wt. %, particularly preferably  greater than 35 wt. %.
It is preferred, however, first of all to extend the starter compound by DMC-catalysed propoxylation, preferably to a number average molecular weight of between 500 and 15,000 g/mol, and subsequently, from this extended propoxylated intermediate, by DMC-catalysed polyaddition to an ethylene- oxide/propylene oxide mixture in the weight ratio EO:PO of 40:60 to 95:5, preferably 50:50 to 90:10, particularly preferably 60:40 to 90:10, as end block, to produce a long-chain polyether polyol having a high content of primary OH groups and a content of oxyethylene units of  greater than 25 wt. %, preferably  greater than 30 wt. %, particularly preferably  greater than 35 wt. %.
In this case the process according to the invention is particularly preferably carried out as a so-called xe2x80x9cone-pot reactionxe2x80x9d wherein, after the DMC-catalysed propoxylation, without intermediate working up of the polymer containing the DMC catalyst, the polyaddition of the ethylene oxide/propylene oxide mixture as end block is subsequently carried out in the same reaction vessel and with the same DMC catalyst.
The DMC-catalysed polyaddition of the ethylene oxide/propylene oxide mixture as end block to the starter compounds (or to the extended propoxylated intermediates) is generally carried out at temperatures of 20xc2x0 C. to 200xc2x0 C., preferably within the range of 40xc2x0 C. to 180xc2x0 C., particularly preferably at temperatures of 50xc2x0 C. to 150xc2x0 C. The reaction can be carried out at total pressures of 0.001 to 20 bar. The polyaddition can be carried out in bulk or in an inert, organic solvent, such as toluene or THF. The quantity of solvent is conventionally 10 to 30 wt. %, based on the quantity of the polyether polyol to be produced.
The polyaddition can be carried out continuously or discontinuously, for example, in a batch or semi-batch process.
The weight ratio of the ethylene oxide/propylene oxide mixture to be used is 40:60 to 95:5, preferably 50:50 to 90:10, particularly preferably 60:40 to 90:10.
The molecular weights of the polyether polyols having a high content of primary OH groups and produced by the process according to the invention are within the range of between 1,000 and 100,000 g/mol, preferably within the range of 1,500 to 50,000 g/mol, particularly preferably within the range of 2,000 to 20,000 g/mol.
The content of primary OH groups can be determined in accordance with ASTM-D 4273-83, from the 1H-NMR spectra of the peracetylated polyether polyols. The content of primary OH groups in the polyether polyols is 40 to 95 mol%, preferably 50 to 90 mol-%. The content of primary OH groups in the polyether polyols is dependent upon the reaction conditions, such as pressure, temperature and solvent as well as on the composition of the ethylene oxide/propylene oxide mixture used. In general, an increase in the ethylene oxide content in the ethylene oxide/propylene oxide mixture leads to an increase in the content of primary OH groups in the polyether polyol.
The concentration of DMC catalyst is so chosen that an effective control of the polyaddition reaction is possible under the given reaction conditions. The concentration of catalyst is generally within the range of 0.0005 wt. % to 1 wt. %, preferably within the range of 0.001 wt. % to 0.1 wt. %, particularly preferably within the range of 0.001 wt. % to 0.01 wt. %, based on the quantity of the polyether polyol to be produced.
Highly active DMC catalysts render possible the production of long-chain polyether polyols having a high content of primary OH groups with a very low concentration of catalyst (50 ppm or less, based on the quantity of the polyether polyol to be produced). If the polyether polyols produced in this way are used for the production of polyurethanes, a removal of the catalyst from the polyether polyol can be dispensed with, without impairing the product qualities of the polyurethane obtained.